1. Field of the Invention
The present invention refers to a device for measuring or controlling a fluid, in particular the flow rate or amount thereof, and to a method for manufacturing said device.
2. Description of the Related Art
Meters as those referred to are used in various fields, among which devices for metering and mixing liquid ingredients in drink vending machines, known in the field as “post-mix” dispensers; said dispensers typically operate by mixing a given amount of water with a given amount of syrup, so as to supply the desired drink to a user; to this purpose they comprise at least two electric valves, for water and syrup respectively, installed so as to operate together. Said electric valves are generally integrated into one module shaped as one multi-way valve or mixing valve, which can also be removed from the dispenser to maintenance, cleaning, etc. purposes.
In most cases the metering of the two ingredients is carried out by opening for a given time the ducts for water and syrup, which are supposed to be at a constant flow rate, by acting upon a corresponding valve.
In other known solutions (see for instance EP-A-0 607 376), water metering is carried out by calculating its actual amount by means of a flow meter.
At the state of the art “post-mix” dispensers use for metering the amount of water a tangential flow meter, i.e. in which the flow of water is oriented tangentially on the radial blades of the impeller of the meter, i.e. in which the fluid flow is perpendicular to the rotation axis of the impeller. Said meters, commonly fitted into the mixing valve, are bulky and increase the overall size of the valve body; furthermore, they are shaped as a separate part of said valve body, which involves specific sealing fastening operations, for instance by means of a cap placed on said body, also with the risk of deterioration of the washers and subsequent leaks. Furthermore, the maintenance operations on the meter are quite complicated, since the latter is located within the dispenser in such a position that a large part of the mixing valve has to be disassembled to this purpose.
Axial flow meters are also known, i.e. in which the flow of the fluid to be measured is let in with a substantially axial direction with respect to the impeller and/or to the duct into which the latter is fitted, which are generally smaller than the aforesaid tangential meters. Such a device, i.e. an axial device, designed to be used in household washing machines and in water supply systems, is known for instance from EP-A-0 599 341.
The use of axial flow meters, however, is usually not recommended in case of very low liquid flow rates, which means that today they are not used in electric valves operating in such conditions, and in particular in valves for post-mix dispensers as previously referred to, which are characterized by low flow rates.